Research carried out by this group on totally synthetic macrocyclic complexes has led to models which mimic important features of the active site of heme-containing monooxygenase enzymes exemplified by the cytochrome P450 family. These models have been shown to bind both organic substrates, through hydrophobic interactions, and the dioxygen molecule. This produces a ternary complex like that implicated in the catalytic action of cytochrome P450. The unique features of this synthetic ternary complex are the subject of ongoing studies by a variety of synthetic and analytical techniques. Recent NMR studies in these laboratories show that a large number of aliphatic and aromatic guests can be accommodated, regiospecifically, within the permanent cavity of the host, even in the presence of bound 0/2. The mutual interactions of these simultaneously bound species will be studied. Ultimate goals are directed toward the activation of bound 0/2 and the substrate specific, regiospecific, and stereospecific oxygenation of substrates. Reactive intermediates generated by oxygen atom donors are under study in attempts to contribute to the understanding of 0/2 activation. High valent oxometal complexes are of special interest in this regard. Experiments are being directed toward the study of the interconversion between coordinated peroxide in species such as FeIII (0/2/2-) and high valent oxometal species such as (Fe0)3+ because this process is essential to the activation process for the monooxygenase enzymes.